This invention relates to an improvement of a drum brake for vehicle use. More particularly it is aimed at the effective retention of a substantially U-shaped return spring, used in an automotive drum brake being anchored between a pair of brake shoes (hereinafter simply called shoe), by means of an ingenious use of a brake component member, for the purpose of reducing or eliminating rattles of the return spring, i.e., prevention of undesirable noises.
In a drum brake, wherein a pair of crescent-shaped shoes with a lining attached thereon are slidingly urged, by actuation of a wheel cylinder disposed between one end portion of each shoe, onto a drum which rotates with a wheel to brake the vehicle, the pair of shoes which have been contacting the drum must be rapidly and positively retracted therefrom as soon as the actuating force of the cylinder disappears. For this purpose a return spring is anchored between the pair of shoes in order to bias the same, by means of the elasticity of the spring, in a direction of withdrawing them from the drum, i.e., in a direction of drawing them toward each other.
As a return spring for this purpose, a substantially U-shaped spring made of a rigid wire rod is used, as opposed to a coil type spring. Particularly in case of a small type drum brakes a U-shaped return spring is preferable to a coil spring because of its considerably free choice of positioning without fear of being affected by other brake component members.
Because the return spring is engaged only at the end portion of the shoes, the central curved or loop portion of the spring is liable to move irregularly or rattle due to vibration of the vehicle or other causes thereby hitting other brake component members and giving rise to a so called rattling sound in the brake system or some other undesirable sound. It is also a serious problem that as a result of such rattling the return spring may contact the brake drum which is rotating in confrontation therewith, thereby increasing the wear and reducing the effectiveness of both the return spring and the brake drum. Because of the difficulty of mounting a suitable means to restrain the rattling within the considerably narrow space of the brake system, no effective means has been found in the prior art to control this problem.
Although a device for retaining the return spring by means of a hair pin spring disposed at a central portion of the return spring has been disclosed in U.S. Pat. No. 3,853,207, it is a shoe hold down spring (a spring which is engaged with the end straight line portion of the return spring), rather than the hair pin spring, that is really effective in the retention or cramping down of the return spring. Even this patented construction of the return spring still contains various problems such as:
(1) The U-shaped return spring is kept down or held down onto the shoe webs, resulting in rubbing and the consequent deterioration of the spring function.
(2) The hair pin spring in that patent is separately made and attached to each shoe, thereby increasing the number of component members, raising the manufacturing cost, and complicating the assembling operation.
To overcome such shortcomings, after having made many studies on the retention of the U-shaped return spring, the inventor thought of controlling the movement of the U-shaped return spring by utilizing a part of the anchor present in the type of drum brake wherein the pair of shoes abut on an anchor at the end portions thereof opposite the end portions actuated by the wheel cylinder. The curved or loop portion of the U-shaped return spring is placed on the anchor.
After further study the conclusion was reached for solving the various problems, of the prior art by which a part of an anchor bracket, which is an anchor component member which is flexible or adaptable for being formed into several shapes is formed into a return spring supporter; consequently the rattling of the spring is controlled, the wearing of the spring is eliminated, and the increase of component members is completely avoided.